Diamond has excellent characteristics such as high heat conductivity, high carrier mobility, high dielectric breakdown electric field, low dielectric loss, and the like, and has been widely used for a cutting tool, an abrasion-resistant tool, and the like due to its incomparable high hardness. Conventionally, natural single-crystal diamond or single-crystal diamond synthesized by a high-temperature/high-pressure method has been used widely; however, a thick, freestanding single-crystal diamond can be synthesized by chemical vapor deposition (CVD) in recent years, so that the above-described various applications are expected.
Wide researches have been conducted to achieve high quality of such a CVD single-crystal diamond. For example, in Yamamoto et al., “X-ray topography of homo-epitaxial diamond”, Extended Abstracts (The 51st Spring Meeting, 2004); The Japan Society of Applied Physics and Related Societies, Mar. 28, 2004, No. 2, p. 635 (Non-Patent Document 1), distribution of defects such as dislocations is observed through X-ray topography for a homo-epitaxial diamond obtained by CVD. Moreover, Japanese National Patent Publication No. 2004-503461 (Patent Document 1) discloses a high-quality single-crystal CVD diamond layer having a thickness of more than 2 mm as well as a method of generating the single-crystal CVD diamond layer, wherein the single-crystal CVD diamond layer is synthesized through CVD after decreasing a defect density in a surface of a diamond base serving as a seed substrate in order to obtain a single-crystal CVD diamond having an excellent electronic property.